Refactor vp10_drl_idx concept

Remove the implicit assumption on offsetting the index by 1.

Change-Id: I2d2b9848916e16723fddd58e7a15e4e7ac4963e3

av1/common/mvref_common.h

@@ -354,16 +354,16 @@ static int16_t av1_mode_context_analyzer(const int16_t *const mode_context,
 
 static INLINE uint8_t av1_drl_ctx(const CANDIDATE_MV *ref_mv_stack,
                                    int ref_idx) {
-  if (ref_mv_stack[ref_idx + 1].weight >= REF_CAT_LEVEL &&
-      ref_mv_stack[ref_idx + 2].weight >= REF_CAT_LEVEL)
+  if (ref_mv_stack[ref_idx].weight >= REF_CAT_LEVEL &&
+      ref_mv_stack[ref_idx + 1].weight >= REF_CAT_LEVEL)
     return 0;
 
-  if (ref_mv_stack[ref_idx + 1].weight >= REF_CAT_LEVEL &&
-      ref_mv_stack[ref_idx + 2].weight < REF_CAT_LEVEL)
+  if (ref_mv_stack[ref_idx].weight >= REF_CAT_LEVEL &&
+      ref_mv_stack[ref_idx + 1].weight < REF_CAT_LEVEL)
     return 1;
 
-  if (ref_mv_stack[ref_idx + 1].weight < REF_CAT_LEVEL &&
-      ref_mv_stack[ref_idx + 2].weight < REF_CAT_LEVEL)
+  if (ref_mv_stack[ref_idx].weight < REF_CAT_LEVEL &&
+      ref_mv_stack[ref_idx + 1].weight < REF_CAT_LEVEL)
     return 2;
 
   assert(0);

av1/decoder/decodemv.c

@@ -118,7 +118,7 @@ static void read_drl_idx(const AV1_COMMON *cm,
   mbmi->ref_mv_idx = 0;
 
   if (xd->ref_mv_count[ref_frame_type] > 2) {
-    uint8_t drl0_ctx = av1_drl_ctx(xd->ref_mv_stack[ref_frame_type], 0);
+    uint8_t drl0_ctx = av1_drl_ctx(xd->ref_mv_stack[ref_frame_type], 1);
     aom_prob drl0_prob = cm->fc->drl_prob0[drl0_ctx];
     if (aom_read(r, drl0_prob)) {
       mbmi->ref_mv_idx = 1;
@@ -126,7 +126,7 @@ static void read_drl_idx(const AV1_COMMON *cm,
         ++xd->counts->drl_mode0[drl0_ctx][1];
       if (xd->ref_mv_count[ref_frame_type] > 3) {
         uint8_t drl1_ctx =
-            av1_drl_ctx(xd->ref_mv_stack[ref_frame_type], 1);
+            av1_drl_ctx(xd->ref_mv_stack[ref_frame_type], 2);
         aom_prob drl1_prob = cm->fc->drl_prob1[drl1_ctx];
         if (aom_read(r, drl1_prob)) {
           mbmi->ref_mv_idx = 2;

av1/encoder/bitstream.c

@@ -117,13 +117,13 @@ static void write_drl_idx(const AV1_COMMON *cm,
   uint8_t ref_frame_type = av1_ref_frame_type(mbmi->ref_frame);
   if (mbmi_ext->ref_mv_count[ref_frame_type] > 2) {
     uint8_t drl0_ctx =
-        av1_drl_ctx(mbmi_ext->ref_mv_stack[ref_frame_type], 0);
+        av1_drl_ctx(mbmi_ext->ref_mv_stack[ref_frame_type], 1);
     aom_prob drl0_prob = cm->fc->drl_prob0[drl0_ctx];
     aom_write(w, mbmi->ref_mv_idx != 0, drl0_prob);
     if (mbmi_ext->ref_mv_count[ref_frame_type] > 3 &&
         mbmi->ref_mv_idx > 0) {
       uint8_t drl1_ctx =
-          av1_drl_ctx(mbmi_ext->ref_mv_stack[ref_frame_type], 1);
+          av1_drl_ctx(mbmi_ext->ref_mv_stack[ref_frame_type], 2);
       aom_prob drl1_prob = cm->fc->drl_prob1[drl1_ctx];
       aom_write(w, mbmi->ref_mv_idx != 1, drl1_prob);
     }

av1/encoder/encodeframe.c

@@ -1245,7 +1245,7 @@ static void update_stats(AV1_COMMON *cm, ThreadData *td) {
           uint8_t ref_frame_type = av1_ref_frame_type(mbmi->ref_frame);
           if (mbmi_ext->ref_mv_count[ref_frame_type] > 2) {
             uint8_t drl0_ctx =
-                av1_drl_ctx(mbmi_ext->ref_mv_stack[ref_frame_type], 0);
+                av1_drl_ctx(mbmi_ext->ref_mv_stack[ref_frame_type], 1);
             if (mbmi->ref_mv_idx == 0)
               ++counts->drl_mode0[drl0_ctx][0];
             else
@@ -1254,7 +1254,7 @@ static void update_stats(AV1_COMMON *cm, ThreadData *td) {
             if (mbmi_ext->ref_mv_count[ref_frame_type] > 3 &&
                 mbmi->ref_mv_idx > 0) {
               uint8_t drl1_ctx =
-                  av1_drl_ctx(mbmi_ext->ref_mv_stack[ref_frame_type], 1);
+                  av1_drl_ctx(mbmi_ext->ref_mv_stack[ref_frame_type], 2);
               if (mbmi->ref_mv_idx == 1)
                 ++counts->drl_mode1[drl1_ctx][0];
               else

av1/encoder/rdopt.c

@@ -3266,7 +3266,7 @@ void av1_rd_pick_inter_mode_sb(AV1_COMP *cpi, TileDataEnc *tile_data,
         int ref_idx;
         int ref_set = AOMMIN(2, mbmi_ext->ref_mv_count[ref_frame_type] - 2);
         uint8_t drl0_ctx =
-            av1_drl_ctx(mbmi_ext->ref_mv_stack[ref_frame_type], 0);
+            av1_drl_ctx(mbmi_ext->ref_mv_stack[ref_frame_type], 1);
 
         rate2 += cpi->drl_mode_cost0[drl0_ctx][0];
 
@@ -3320,7 +3320,7 @@ void av1_rd_pick_inter_mode_sb(AV1_COMP *cpi, TileDataEnc *tile_data,
 
           if (mbmi_ext->ref_mv_count[ref_frame_type] > 3) {
             uint8_t drl1_ctx =
-                av1_drl_ctx(mbmi_ext->ref_mv_stack[ref_frame_type], 1);
+                av1_drl_ctx(mbmi_ext->ref_mv_stack[ref_frame_type], 2);
             tmp_rate += cpi->drl_mode_cost1[drl1_ctx][ref_idx];
           }